Yami Marik, known as Dark Marik in the manga and Japanese versions, is the second personality created by Marik Ishtar's hatred. He serves as the main antagonist of the Battle City arc after Odion falls into a coma, triggering his take over of Marik's body.
Yami Marik's usual outfit consists of a long purple cape with a gold chain (similar to one worn by the Rare Hunters), a sleeveless black shirt and khaki pants. He wears gold earrings, neckwear, armbands and bracelets up his wrists. His hair is spiked upwards and points in all directions and he bears the Eye of Wdjat on his forehead. Whilst dueling, faint, ghastly images of his face frequently stretch out from his head. In the Battle City arc he often wears a KaibaCorp Duel Disk on his left arm.
Yami Marik is a person of pure cruelty and insanity who cares for no one but himself, as he was born of hate, anger, and envy. Yami Marik ruthlessly murdered his father, and was constantly trying to kill Odion for being a hindrance to his existence in the outside, and threatened Ishizu with death for hiding their brother. Yami Marik showed no interest for Yami Yugi's past or Seto Kaiba's past, something which his alter ego wanted to know. In the original Japanese version Dark Marik has no specific goals (save for killing Yugi) he simply enjoys destruction and killing. In the English dub anime, he wanted to rule the world.
Aside from his lack of empathy, he also seems to be a sadist, building his Deck around torture-themed cards, and using the shadow powers to manifest them into reality, painfully hurting his opponents for his own pleasures. He even became dependent on his dark powers to win his duels, since he wouldn't have won his duel against Mai Valentine right away, if it wasn't for Ra's Sphere Form, and in his duel against Joey Wheeler, he could have lost if Joey hadn't collapsed because of the torturing of Marik's "The Winged Dragon of Ra".
In Noah Kaiba's Virtual World fortress, Dark Marik showed that he can be a reckless person, as he destroyed the fortress' computer, the only way of stopping a missile is programmed to fire at the place.
Despite his cruelty and evil, he valued his own life dearly, and tried to kill Odion so he would not be sealed back in. He also tried to plead for Marik to help him win against Yugi after Marik was able to gain control of his body. Still, he shows traits of a masochist as well, especially in the Japanese version of his duel against Joey. For example, after his "Gil Garth's" pain was transferred to him, he laughed scabrously and stated that he was enjoying the feeling.
Yami Marik was "born" from the pain that Marik had endured when he was forced to take the initiation ritual to become a full Tombkeeper at ten years old by his father. A year later, Yami Marik emerged for the first time (after Marik's forbidden trip to surface) to resist his father's punishment and claim the Millennium Rod for himself. Ignoring his father's orders to put the item down, Yami Marik used its powers to smash him against the wall. When his sister Ishizu protested, she suffered the same strike. Yami Marik then proceeded to murder his father. In the manga, Yami Marik specifically skinned his father with it and then threw his father's back onto his adopted brother, Odion. In the Japanese anime, he killed his father to stop him from killing Odion (in the English anime he sent his father to the Shadow Realm). Yami Marik was then sealed away in Marik's body by Odion.
Yami Marik was released during the Battle City quarter-finals when Odion was rendered unconscious during his duel against Joey Wheeler. In Marik's quarter-final match, Yami Marik duels and defeats Mai Valentine in aShadow Game using "The Winged Dragon of Ra". After winning, Yami Marik traps Mai's soul where several brain insects slowly devour her body (in the English version, he banished her soul to the Shadow Realm). After this, Joey is determined to duel Yami Marik and save Mai no matter how high the cost.
After the quarter-finals, Yami Marik defeats Yami Bakura in a match not part of the tournament (who teams up with the real Marik's soul), gaining the Millennium Ring as the "spoils of war".
In the Virtual World arc, Marik stays on the blimp for most of the arc, but he eventually gets tired of waiting and looks around in Noah's base to find Yugi and his friends. He uses the power of his Millennium Rod to wipe out any obstacles in his way and wrecks the computer that controls the satellite which fired the missile that destroyed the base. Marik and all the others managed to get out in time.
The next day, he duels Joey during the semi-finals, who manages to gain the upper hand until Marik summons "Ra". However, Joey is still standing after Ra's blast and Summons "Gearfried the Iron Knight", a monster with enough power to win him the duel. He attempts to attack Marik directly but collapses from the Shadow Game and is unable to continue to claim victory. As time goes on, Yami Marik becomes the dominant host of Marik's body, with the real Marik's soul slowly fading out of existence. Yami Marik turns his duel with Yami Yugi in the finals into a Shadow Game that gives him a clear edge; when Yami Yugi lost Life Points, Yugi Muto's body would fade away, and when Yami Marik lost life points, the original Marik would fade away. While they duel, Odion wakes up and makes Marik realize that he has to accept his responsibility for being a Tombkeeper. With this confidence, Marik overpowers his evil self and forfeits, destroying Yami Marik.
Yami Marik makes another brief appearance in Mai's nightmares at the beginning of Waking the Dragons.
Yami Marik appears in two flashbacks in Yu-Gi-Oh! GX. When Syrus Truesdale mentions some of Yugi's exploits and tells Jaden Yuki about the Egyptian Gods and when Franz uses the counterfeit copy of "The Winged Dragon of Ra".